1. Field of the Invention
The present invention relates to a seismic actuator, and in particular to a device capable of initiating various actions and/or changes to a system in response to seismic activity above a predetermined threshold level.
2. Description of Related Art
A significant source of damage during earthquakes are fires caused by the rapture of natural gas lines due to the seismic activity. Natural gas is widely used in residential homes for heating and cooking due to its convenience, cleanliness and efficiency. However, natural gas is highly flammable and fires resulting from gas escaping a ruptured gas line during an earthquake can often cause more damage than the seismic shockwaves themselves.
In order to prevent fires from ruptured gas lines during an earthquake, several devices have been developed for automatically shutting off the flow of gas within a gas line upon seismic activity above a threshold level. For example, U.S. Pat. No. 4,960,147 to Diamond discloses a shock-activated valve including a valve assembly and a pendulum and ball detent assembly. The valve assembly includes a handle biased via a spring from an open position where gas is allowed to flow to a closed position where gas flow is shut off. The handle is held in the open position by engagement with a ball protruding out of the top of the pendulum and ball detent assembly. The ball is held in engagement with the handle by resting on top of an upper portion of a pendulum. During seismic activity, the pendulum swings thereby allowing the ball to drop within the assembly. Once the ball disengages from the handle, the handle is free to swing to the closed position to shut off gas flow.
Another example of a seismic valve is disclosed in U.S. Pat. No. 4,860,780 to Fisher, which shows a pendulum having a trigger portion with a flat upper surface normally parallel to a lower surface of an activator. During seismic activity, the pendulum swings thereby causing the flat upper surface of the trigger to raise up, contact, and lift the activator. The activator normally holds a control lever in an open position. Upon the activator being raised, the control lever is free to swing closed due to the biasing force of a spring, to thereby shut off gas flow.
U.S. Pat. No. 4,131,124 to Sunde discloses a disk mounted on a stem within a gas flow tube. The disk is biased via a spring into a position over a port which would block gas flow. The disk and stem are held in an open position via a pivoting rod. Upon seismic activity, the pivoting rod pivots, thereby freeing the stem and disk to move downward over the port to shut off gas flow.
U.S. Pat. No. 5,482,074 to Hanson discloses a spool member within a gas flow line. The spool member is biased via a spring into a position blocking gas flow, but is held in an open position via a trigger assembly. Upon seismic activity, a pendulum oscillates such that a flange of the pendulum engages the trigger assembly to move the trigger assembly downward, thus freeing the spool member to move to a position to shut off gas flow.
U.S. Pat. No. 3,890,993 to MacNeilage discloses a pendulum having an upper end including a recess which engages an arm. The arm is biased into a position which would shut off gas flow, but is held in an open position by the recess in the upper end of the pendulum. Upon seismic activity, the recess disengages from the arm so that the arm swings to the position where gas flow is shut off.
Several other patents disclose gravity-based shut off valves where a ball covers a valve, or otherwise causes a valve to close, upon the ball being unseated from its support position by seismic activity, and falling to a lower potential energy state. See, for example, U.S. Pat. No. 4,091,831 to Pazmany; U.S. Pat. No. 4,885,832 to Plemmons et al.; and U.S. Pat. No. 5,209,252 to Perle. Still other patents disclose seismic valves including magnetically held objects, which objects fall into a position blocking gas flow upon the object being shaken loose from the magnet due to seismic activity. See, for example, U.S. Pat. No. 4,817,657 to Kovacs and U.S. Pat. No. 5,240,025 to Morris.
Some references further disclose a reset mechanism for resetting the valve after the valve moves to a position blocking gas flow. See, for example, U.S. Pat. No. 4,485,832 to Plemmons et al.; U.S. Pat. No. 5,209,252 to Perle; and U.S. Pat. No. 4,799,505 to Nowell.